Evaluation of Total Phenolic Compounds, Alkaloids and Proanthocyanidins Contents and Antioxidant Activity in Three Onosma Species (Boraginaceae) From Iran

The genus Onosma L. is one of the important genera of the family Boraginaceae. In flora Iranica, the genus comprises 55 species, of which 17 are endemic to Iran. Onosma species contain secondary metabolits that represent antioxidant and antibiotic activities. Methanolic extracts of three Onosma species, namely Onosma pachypoda L., Onosma sericea L.and Onasma microcarpa DC. from flora of Iran were in vitro screened for their total phenol, flavonoid, proanthocynidin and alkaloid contents and also their possible antioxidant activities by different tests. Results showed that the methanolic extract of Onasma microcarpa contained the highest amount of total phenols. Onosma pachypoda and Onosma sericea represented the highest flavonoid content. Results also showed the highest amount of alkaloid and proanthocyanidin in Onosma sericea and Onosma pachypoda, respectively. In addition, methanolic extracts of the three Onosma species showed strong antioxidant activity and Onosma microcarpa represented the lowest IC50. It seems that phenolic compounds are the substances that play an important role in antioxidant activity.